Positioning and fixing devices of various types have been proposed and are currently supplied for use that position and fix, on a table of a machining center or the like, a workpiece pallet that is provided for fixing, conveying, and positioning a workpiece in the machining center or the like. As positioning devices of this type, there are employed both an all-direction positioning device that positions the workpiece both in an X direction and in a Y direction within the horizontal plane, and a one-way positioning device that is only capable of positioning the workpiece horizontally in a first direction, while permitting shifting in the other direction.
When a workplace is to be positioned precisely within the horizontal plane, since pitch errors in the distance between a pair of cylindrical holes in the workpiece may arise during machining for forming the holes, accordingly one of the cylindrical holes is positioned with an all-direction positioning device, and then, in order to absorb the error in pitch, the other cylindrical hole is positioned with a one-way positioning device.
The positioning device described, in Patent Document #1 comprises a main body member, a plug portion that is formed to project upward above the top of the main body member, taper shaped positioning portions (i.e. tapered portions) that are formed on opposite side portions of the external peripheral portion of the plug portion so as to sandwich its axis between them and that reduce in diameter upward, a tapered sleeve that is fitted over the tapered portion of the plug member, a drive rod that is passed through the plug portion and the tapered sleeve and to whose upper end portion the upper end portion of the tapered sleeve is integrally connected, and a hydraulic cylinder that is capable of driving the drive rod so as to raise and lower it.
After the plug portion and the tapered sleeve have been inserted into a hole in the workpiece, the drive rod is driven downward by the hydraulic cylinder so that the tapered sleeve is expanded diametrically and is tightly contacted against the inner circumferential surface of the hole, and thereby it is arranged to position the workpiece so that it is not capable of shifting in a first direction that is orthogonal to a horizontal direction connecting the pair of axes of two of these positioning devices, while being capable of shifting horizontally in a second direction that connects that pair of axes.
The positioning device described in Patent Document #2 (refer to FIGS. 3 and 4 of that publication) has a structure that resembles the positioning device described above, but is built with the plug member being provided separately from the main body member, with a tapered portion that reduces in diameter upward being formed on the external peripheral portion of the plug portion, with a slide flange portion at the lower end portion of the plug member being shiftably installed in a long aperture that is formed in the main body member, and with the drive rod being slightly shiftable in the horizontal direction with respect to the output member of the hydraulic cylinder (i.e. with respect to its piston member); and the plug member, the drive rod, and the tapered sleeve are not capable of shifting in a first direction, but are capable of shifting horizontally in a second direction that is orthogonal to that first direction.
Patent Document #1: JP Laid-Open Patent Publication 2006-7334
Patent Document #2: JP 4,799,487 Patent Publication